Pleistocene Ice Sheets Research Articles

Palynomorphs of ice rafted clastic sedimentary rocks in Late Quaternary glacial marine sediments of the Norwegian Sea as provenance indicators

Palynomorph assemblages of ice rafted pebbles of clastic sedimentary rocks in surface sediments from 0 to 41 cm depth of the Norweigan Sea are dominated by Triassic and Lower Cretaceous taxa along with occasional Jurassic, Lower Paleozoic, and very rare Carboniferous-Permian taxa. Tertiary species were not found, and Upper Cretaceous species were only found in the western Norweigan Sea. The ice-rafted rock fragments originated from the Late Pleistocene ice sheets adjacent to the Norwegian Sea. The determined ages of the ice-rafted clastic sedimentary rocks indicate the Barents shelf as the main source, because the Barents shelf has exposures of clastic sedimentary rocks whose ages and lithologies match the material found in the majority of the analyzed samples. In addition some material originated from the West Norwegian shelf and some from NE Greenland. Our results confirm that an ice sheet extending from SW Svalbard onto parts of the northwestern Barents shelf existed during the Late Weichselian. The northern dropstone source areas suggest that currents in the Norwegian Sea from 15 to 9 ka before present were moving in the opposite direction of modern currents

The Quaternary history of the subtidal central Wash, eastern England

The history of Quaternary sedimentation in the subtidal Wash is described using high-resolution seismic profiles. The Pleistocene sequence is divided into three depositional units, comprising Anglian till overlain by possible Late Devensian subglacial scour fill and lacustrine sediments. These latter sediments may provide further evidence for a lake in the Wash impounded by ice along the Lincolnshire–Norfolk coast. The Holocene sequence is divided into six depositional units, each truncated by the one above. Estuarine sediment resting on a marine flooding surface forms the earliest unit. This sediment was partially eroded by migration of the shoreface as the marine flooding progressed landward. The following four units comprise sand and gravel banks deposited on the erosion surface. Bank deposition was followed by an episode of tidal scour caused either by increased tidal current velocities following reclamation of the Fenland or by breakdown of postulated former offshore barriers. The youngest and most extensive Holocene unit rests on the scoured surface and comprises several types of deposit. These are: large sand banks around the periphery of the subtidal area with sediment extending seawards into two NE–SW aligned troughs; low sand banks on a central ridge dividing the troughs and partially covering the sediments in the troughs; thick gravels towards the mouth of the Wash; muddy sediments forming drapes over the sand in the centre of the Wash. The data provide information on the variety of processes related to the advance and retreat of Pleistocene ice sheets in eastern England and the subsequent Holocene marine flooding of the Wash–Fenland embayment. The Holocene sequence reveals periods of widespread sedimentation separated by periods of both local and regional erosion, with possible implications for climatic and hydrodynamic change. © 1997 John Wiley & Sons, Ltd.

Global postseismic rebound of a viscoelastic Earth: Theory for finite faults and application to the 1964 Alaska earthquake

A spherically symmetric Earth model with viscoelastic rheology is used to study the postseismic rebound associated with finite lithospheric dislocations. We perform a systematic study of surface deformations due to sources characterized by two‐ and three‐dimensional faults, modeled by a linear and planar distribution of point sources. Our approach is based on the normal mode technique for a layered Earth with linear viscoelastic rheology and allows for a self‐consistent description of the time evolution of postseismic displacements due to strike‐ and dip‐slip faults. As a case study, we compare the predicted horizontal displacements due to the 1964 Alaska earthquake with very long baseline interferometry (VLBI) baselines changes observed in this region in the period 1984–1989. Although subduction and postglacial isostatic adjustment are expected to contribute significantly to present‐day velocities, our results show that the postseismic rebound due to the 1964 Alaska earthquake plays a relevant role in the changes of several VLBI baselines. The last section is devoted to the analysis of the evolution of other North American baselines. As suggested by recent investigations based on forward approaches, isostatic readjustment of the Earth's crust in response to the melting of the last Pleistocene ice sheets is a major contributor to baseline variations in this area. Our results indicate that a correct interpretation of VLBI baseline changes in North America should account also for the effects of postseismic deformation.

Rock weathering in blockfields: some preliminary data from mountain plateaus in North Norway

Abstract The formation of blockfields is a process usually attributed to weathering. In mountain areas this is generally assumed to be mechanical weathering (frost shattering). Evidence from two high plateaus [900 and 1350 m above sea level (a.s.l.)] in North Norway ( c. 70°N) suggests that chemical action is at least as important as mechanical activity in blockfield formation. The bedrock in both areas consists of complex banded gabbros. Blockfields circumscribe ice masses and are generally > 1 m thick. They contain high percentages of material in the silt and clay sized fractions, including a variety of clay minerals: gibbsite, chlorite, vermiculite and kaolinite, as well as magnetite/maghemite. The blockfield thickness and presence of these weathering products suggests both a considerable (pre-Pleistocene) length of time required for development as well as warmer conditions than are found now (mean annual air temperature c. 0°C) or in the period since deglaciation. It is suggested that these blockfields represent a preglacial palaeosurface which formed initially under warmer conditions and has survived, largely intact, beneath all the Pleistocene ice sheets.

Somes Sound: Fjord or Well-Mixed Estuary?

Somes Sound has been described as the only example of a fjord on the east coast of the United States. On a small scale, and from a morpho? logical point of view, the Sound has key features normally associated with fjords, including pronounced subaerial topographic relief, submarine sills, and the U-shaped cross-section typical of glacially-carved troughs. However, based on its salinity distribution, which is related to the mixing and circulation processes used to characterize estuarine types from an oceanographic point of view, Somes Sound is a vertically well-mixed estuary that does not exhibit the strong stratification typical of fjords. While its geomorphology is unique, the oceanographic processes operating in the embayment are essentially the same as those in other shallow Maine estuaries with low fresh water input. In these estuaries, as well as in Somes Sound, tidal mixing is dominant over freshwater inflow in determining the circulation and the vertical stratification of the water column. Somes Sound, a narrow cut that nearly divides Mount Desert Island in two (Fig. 1), is morphologically unique among coastal embayments and estuaries along the eastern seaboard of the United States. The coastal embayments of Maine were altered by glacial erosion of the Pleistocene ice sheets and postglacial changes in sea level creating the typical low rolling relief best characterized as a fjard or firth coastline (Belknap et al. 1986; Kjerfve 1989). On the other hand, topographic relief in the Mount Desert region is decidedly more pronounced, and the eastern shore of Somes Sound rises at one point to more than 250 m above sea level. In addition to the spectacular subaerial relief, the submarine topogra? phy of the Sound displays the U-shaped channel cross-section and shallow terminal sill that characterize glacially-carved and deepened valleys. Based on these and other geological characteristics, Johnson (1925) concluded that Somes Sound represents the only possible ex? ception to the statement that the term fjord cannot be properly applied to the coast of Maine. * Department of Oceanography, University of Maine, Orono, ME 04469-5741; ** Bigelow Laboratory for Ocean Sciences, West Boothbay Harbor, ME 04575 This content downloaded from 157.55.39.178 on Fri, 05 Aug 2016 04:51:03 UTC All use subject to http://about.jstor.org/terms 36 Northeastern Naturalist Vol. 4, No. 1 Figure 1. Mt. Desert Island

A ring-shear device for the study of till deformation: Tests on tills with contrasting clay contents

Deformation of subglacial sediment may have had a profound influence on the geomorphic effects and dynamics of Pleistocene ice sheets, but data that bear on the rheology of such sediment are few and contradictory. A means of studying systematically the mechanical properties of glacial tills is provided by a ring-shear device that shears a large annular specimen to high strains at variable rates. Special features of the device allow continuous observation of the distribution of shear strain, measurement of local stresses normal to the direction of shear, and isolation of wall effects. Thus far, a linear-viscous putty and two tills with different clay contents (4 and 32% by weight) have been tested. The experiments with till indicate, as expected, that the presence of dispersed clay minerals reduces markedly both the residual strength and hydraulic diffusivity of till. Clay also reduces spatial variations in normal stress associated with grain bridges. The walls bounding the specimen support only 9–17% of the total resistance to shearing. Strain was localized in both tills, but not in the linear-viscous putty. Strain localization in the tills indicates that their theology departs significantly from linear- and Bingham-viscous models.

Postglacial sea-level change on a rotating Earth: first results from a gravitationally self-consistent sea-level equation

We present and solve a gravitationally self-consistent sea-level equation which governs postglacial sea-level variations on a spherically symmetric, self-gravitating, viscoelastic and rotating Earth. We find that the inclusion of a glacio-isostatically induced rotational excitation can significantly affect previous predictions of both present-day sea-level rates and postglacial sea-level histories which were based on a theory that assumed a non-rotating Earth model. To illustrate, we consider present-day sea-level rates (and tide-gauge corrections) along the US east coast, and relative sea-level curves in the far field of the late Pleistocene ice sheets.

The influence of a finite glaciation phase on predictions of post-glacial isostatic adjustment

We predict relative sea level (RSL) variations, present day three-dimensional (3D) crustal deformation rates and baseline velocities, and a set of anomalies in the gravitational field of the planet, using a suite of models for the space-time geometry of the Pleistocene ice sheets. These models are distinguished on the basis of the details of the glaciation phase, and they include the cases of an infinite glaciation phase (i.e., an assumption of isostatic equilibrium at the time of the last glacial maximum — LGM), a steady uniform glaciation, and a glaciation in which the bulk of the accumulation is limited to the final stages of the growth phase. Comparison of the observational records of postglacial RSL change with predictions based on the assumption of isostatic equilibrium at LGM have commonly been used to infer both the space-time geometry of the final deglaciation event and the mantle viscosity. We conclude that both these applications may be influenced significantly by the incorporation of a finite glacial cycle. As an example, RSL predictions, which assume isostatic equilibrium at LGM, and those which incorporate a relatively rapid glaciation phase, can differ by a factor of 2 or more at some sites within previously glaciated regions when an Earth model characterized by a lower mantle viscosity of 10 22 Pa s is adopted. We have also found that differences in the adopted model for the glaciation event are capable of explaining entirely the discrepancies ( ∼ 0.2 mm/yr) between previously published predictions of present day tangential velocities in North America. These discrepancies are characterized by a dominant long-wavelength signal and, hence, they do not necessarily influence (strongly) predictions of baseline velocities. Variations in the glaciation model can also have an important effect on predictions of peak gravity anomalies over previously glaciated regions, and secular variations in the zonal harmonics of the Earth's geoid. In both cases the effect may be sufficient to alter significantly the signal from other geophysical processes which may need to be invoked to reconcile the observational constraints.

Present‐day post‐glacial sea level change far from the Late Pleistocene ice sheets: Implications for recent analyses of tide gauge records

We examine the sensitivity of predictions of the present‐day rate of sea level change due to glacial isostatic adjustment (GIA) in two regions located within the ‘far‐field’ of the Late Pleistocene ice sheets (Europe/north Africa and the western Pacific/Caribbean) to variations in the mantle viscosity profile. The regions considered here encompass the location of 11 (of 21) sites used in a recent determination, based on GIA‐corrected tide gauge records, of the global rate of secular sea level change. Our analysis suggests that the mean GIA correction at the 11 far‐field sites may vary by as much as 0.5 mm/yr, depending on the adopted Earth model, and we derive a bound on the (residual) secular sea level rise of 1.1 to 1.6 mm/yr. This bound is consistent with our analysis of the tide gauge record from the U.S. east coast, and it suggests that previous estimates of the residual sea level rise represent an upper bound.

Glacial drainage towards the Mediterranean during the Middle and Late Pleistocene

To a varying degree the Middle and Late Pleistocene ice sheets in northern Eurasia redirected the drainage of major catchments in Europe and western Siberia from the North Sea and Arctic Ocean south to the Caspian, Black Sea, and ultimately the Mediterranean. During the Late Weichselian, glacial meltwater reached the Mediterranean through the Dniepr and Don catchments and to a minor extent through the Danube. During the Warthe Substage of the Saalian, meltwater from the Volga was most likely added. During the Drenthe Substagc of the Saalian the watershed shifted Par to the east, and meltwater reached the Mediterranean also from the Oh. Irtysh, Yenisei, and Tunguska catchments in Siberia. Depending on the extent of the ice sheets, the increase in freshwater supply during deglaciations resulted in reductions of Mediterranean overflow into the North Atlantic. Such overflow reductions may have reduced vapour transport to the ice sheets and thus accelerated wastage.

Deglacial land emergence and lateral upper-mantle heterogeneity in the Svalbard Archipelago-I. First results for simple load models

The glacial-isostatic adjustment following the removal of the Pleistocene ice sheets furnishes basic information on the thickness of the Earth's lithosphere and the viscosity of the subjacent mantle. Paper I is concerned with an elementary interpretation of the post-glacial land emergence observed at a restricted set of six locations in the Svalbard Archipelago. The interpretation is based on a three-layer, incompressible Maxwell-viscoelastic earth model, which is forced by a time-dependent load distribution simulating the deglaciation history of the Svalbard Archipelago and the Barents Sea. In view of inconclusive geomorphological evidence suggesting either total or partial glaciation of the area at glacial maximum, two simple load models, BARENTS-T1 and BARENTS-P1, are considered in the first instance. A comparison between the calculated and observed values of land emergence suggests increases in lithosphere thickness and asthenosphere viscosity with increasing distance of the location from the continental margin. The trends are qualitatively insensitive to the load model, load thickness or load cross-section used. For load model BARENTS-T1 with parabolic cross-section, an initial load thickness of 1.50 km and a relaxed fitting criterion, the lateral variations are only weak. If a more restrictive fitting criterion is employed, the variations become more prominent and suggest increasing values of lithosphere thickness from below 80 km to above 140 km and of asthenosphere viscosity from below 3 × 1018 Pa s to above 2 × 1019 Pa s over a distance of about 300 km. In Paper II (Kaufmann & Wolf 1995), a high-resolution load model and an extended set of land-emergence observations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the Svalbard Archipelago.

The role of hydro-isostasy for Holocene sea-level changes in the British Isles

The last deglaciation of the British ice sheet in combination with melting of more distant ice sheets gives the nearby region a complicated sea-level history, with post-glacial rebound occurring over Scotland and northern England, eustatic sea-level rise much further away, and more complex changes in the intermediate regions like southern England. At the glacial maximum, most of the present North Sea floor was above sea level, and it has subsequently been covered by water. In most previous sea-level calculations, the meltwater load has usually been modelled without allowing for the change in ocean shape as sea-level changes, and frequently without including spatial variability of the meltwater load. By assuming the shoreline was at its present position throughout the period of deglaciation of the Late Pleistocene ice sheets, the amount of tilting of the British Isles by the meltwater load is reduced, since such a model erroneously applies loads both to the east and west of the British Isles. A review of the various meltwater models is included and it is shown that errors in predictions of sea-level change of up to 10 m at 10 kyr B.P. are made along the east coast of England and along the coastlines on the southern edge of the North Sea. The most important effect of the meltwater load is to tilt the continent normal to the continental margin. This pattern is modified by the unloading brought about by glacial rebound of Scotland and the Norwegian coast, and the recent filling with water of the North Sea.

Drumlins in ice sheet reconstructions, with reference to the western Pennines, northern England

Drumlin morphology and distribution can be used to determine the palaeoglaciological conditions under which subglacial bedforms were created by Late Pleistocene ice sheets. Detailed field mapping of part of the large drumlin fields in northern England, in particular the identification of areas of superimposed drumlins, has been shown to be of significance in the delimitation of the ice divide within the area. The overall distribution of the subglacial bedforms has also been used to define the extent of ice streams within this part of the Late Devensian (Dimlington Stadial) ice sheet. Based on the physical principles which underlie the deformational model of drumlin formation and present-day glaciological information on subglacial ice sheet conditions, variations in drumlin morphology have allowed a first attempt at reconstructing areas of high (> 100 kPa) and low (< 20 kPa) basal driving stresses for this part of the ice sheet.

Morphology and seismic stratigraphy of the inner continental shelf off Nova Scotia, Canada: Evidence for a −65 m lowstand between 11,650 and 11,250 C14 yr B.P.

Nova Scotia's position near the margin of large Pleistocene ice sheets makes the Scotian Shelf region critical for evaluation of glaciation models and sea-level change. The sea floor of the inner Scotian Shelf was mapped using multibeam bathymetry, a combination of conventional seismic and sonar techniques, and sampling. Multibeam bathymetry provides an areal image of the sea floor. Combining this unique image with sub-bottom seismic imaging, the relationships between sea floor topography and the underlying strata were explored.The inner continental shelf of Nova Scotia can be subdivided into five major terrain “zones”. These are the: (1) Truncation Zone, (2) Morainal Zone, (3) Outcrop Zone, (4) Basin Zone and (5) Scotian Shelf End-Moraine Complex. The Scotian Shelf End-Moraine Complex and Basin Zone are glacial-depositional zones at the seaward edge of the inner shelf. Landward of these zones is a region of high relief bedrock, with ridges and valleys largely devoid of surficial sediments extending from 80 to 120 m water depth (Outcrop Zone). This zone is interpreted as a relict bedrock surface, preserved under frozen-bed glacier conditions. To the east of the Outcrop Zone, in similar water depths, are unmodified till ridges overlying bedrock (Morainal Zone). The Truncation Zone is a region of the inner shelf from −90 m to the present shoreline characterized by muted acoustic topography and planar erosional surfaces truncating bedrock and surficial sediments. The Truncation Zone is subdivided into the Valley Subzone, the Transition Subzone, the Platform Subzone and the Estuarine Subzone. The Valley Subzone is typified by sediment-infilled valleys occurring in 75 to 90 m water depths. These valleys contain seismic facies with a ponded style of deposition planed off at the sea floor or by erosional unconformities near the sea floor. The Transition Subzone is marked by a relatively steep “ramp” and terraces. The ramp at the type section extends from 75 to 65 m water depth. The surface of the ramp can be either an erosional unconformity or a depositional surface formed by clinoform beds. The −65 m former shoreline is interpreted as the top of the Transition Subzone ramp surface. At one ramp locality, clinoform beds form part of a progradational sequence called the Sambro Delta. A mussel valve fragment (Mytilus edulis) was obtained from a core in the foresets and radiocarbon dated. An age of 11,650 ± 110 yr B.P. was obtained, adjusted for isotopic fractionation. Above −65 m the sea floor forms a low relief, gently sloping erosional surface (Platform Subzone). Estuarine deposits have been found above −50 m.The new sea-level curve constructed with the dated −65 m shoreline and recently published data is at variance with calculated RSL curves based on geophysical models, primarily in the amplitudes and rates of RSL change. Reasons for the discrepancies may be late-melting ice and regional variations in lithospheric strength and thickness.

Upper Quaternary Sea Levels, Coral Terraces, Oxygen Isotopes and Deep-sea Temperatures.

There are two widely used sea level curves for the last glacial cycle, one based on coral terraces at Huon Peninsula (HP) in Papua New Guinea, the other on oxygen isotope data from deep sea cores. Previous sea level estimates from HP are 20-40 m higher than isotopic sea levels for the interval 30-75 ka but new sea level data from HP support the isotopic sea levels. Computer simulations of coral terraces are more similar to observed HP terraces when the computer model is driven by the isotopic sea level curve than by the previous HP sea level curve. HP sea levels and benthic isotope records were used previously to calculate deep sea temperatures through the last glacial cycle the new HP results lead to a sharper indication that deep sea temperatures were up to 1.8°C cooler during the last glacial cycle than in the interglacials. The temperature estimates depend on the isotopic composition of Pleistocene ice sheets. However, if deep sea temperatures did not change, the HP sea levels require unrealistically low oxygen isotope values for the Pleistocene ice sheets. The model of cooler deep sea temperatures during glacial cycles is adopted here and was used to derive isotopic sea level changes using the V19-30 record over the last 330 ka. The isotopic sea levels before the last interglacial are consistent with the limited data available but need to be tested by high quality data from older coral terrace sequences.

Channelized subglacial drainage over a deformable bed

AbstractWe develop theoretically a description of a possible subglacial drainage mechanism for glaciers and ice sheets moving over saturated, deformable till. The model is based on the plausible assumption that flow of water in a thin film at the ice-till interface is unstable to the formation of a channelized drainage system, and is restricted to the case in which meltwater cannot escape through the till to an underlying aquifer. In describing the physics of such channelized drainage, we have generalized and extended Röthlisberger’s model of channels cut into basal ice to include “canals” cut into the till, paying particular attention to the role of sediment properties and the mechanics of sediment transport. We show that sediment-floored Röthlisberger (R) channels can exist for high effective pressures, and wide, shallow, ice-roofed canals cut into the till for low effective pressures. Canals should form a distributed, non-arborescent system, unlike R channels. For steep slopes typical of alpine glaciers, both drainage systems can exist, but with the water pressure lower in the R channels than in the canals; the canal drainage should therefore be unstable in the presence of channels. For small slopes typical of ice sheets, only canals can exist and we therefore predict that, if channelized meltwater flow occurs under ice sheets moving over deformable till, it takes the form of shallow, distributed canals at low effective pressure, similar to that measured at Ice Stream B in West Antarctica. Geologic evidence derived from land forms and deposits left by the Pleistocene ice sheets in North America and Europe is also consistent with predictions of the model.

Channelized subglacial drainage over a deformable bed

AbstractWe develop theoretically a description of a possible subglacial drainage mechanism for glaciers and ice sheets moving over saturated, deformable till. The model is based on the plausible assumption that flow of water in a thin film at the ice-till interface is unstable to the formation of a channelized drainage system, and is restricted to the case in which meltwater cannot escape through the till to an underlying aquifer. In describing the physics of such channelized drainage, we have generalized and extended Röthlisberger’s model of channels cut into basal ice to include “canals” cut into the till, paying particular attention to the role of sediment properties and the mechanics of sediment transport. We show that sediment-floored Röthlisberger (R) channels can exist for high effective pressures, and wide, shallow, ice-roofed canals cut into the till for low effective pressures. Canals should form a distributed, non-arborescent system, unlike R channels. For steep slopes typical of alpine glaciers, both drainage systems can exist, but with the water pressure lower in the R channels than in the canals; the canal drainage should therefore be unstable in the presence of channels. For small slopes typical of ice sheets, only canals can exist and we therefore predict that, if channelized meltwater flow occurs under ice sheets moving over deformable till, it takes the form of shallow, distributed canals at low effective pressure, similar to that measured at Ice Stream B in West Antarctica. Geologic evidence derived from land forms and deposits left by the Pleistocene ice sheets in North America and Europe is also consistent with predictions of the model.

The stratigraphic and sedimentological significance of Late Devensian Ice Sheet surging in Holderness, Yorkshire, U.K.

Amino acid analyses of marine mollusc valves show that the Basement Till of Holderness, Yorkshire, is of Late Devensian age (ca. 20,000 BP) and not pre-Ipswichian (>125,000 BP) as is traditionally supposed. Together with the overlying Skipsea and Withernsea Tills the Basement Till is argued to be a ‘deformation till’ resulting from the repeated onshore surging of Late Devensian ice over a muddy sea floor, and the subglacial transport, attenuation and mixing of marine sediment. Silts on the surface of the Basement Till, yielding 14C dates of 18,500 and 18,240 BP, have been regarded as minimum ages for Late Devensian glaciation in eastern England (e.g. the Dimlington Stadial of Rose, 1985, 1989). The amino acid data presented here indicates that the maximum of the Late Devensian glaciation in eastern England occurred earlier. Sedimentological interpretation of the Late Devensian tills of Holderness as glacially-reworked marine sediments supports previous glaciological models of the British Ice Sheet involving surging of ice lobes along the coast of eastern England. The Basement, Skipsea and Withernsea tills are separated by shallow marine sediments and may be representative of ‘deformable bed’ till facies deposited below Pleistocene ice sheets moving over soft, fine-grained sediments.

Holocene Deglaciation, Sea-Level Change, and the Emergence of the Windmill Islands, Budd Coast, Antarctica

A Holocene deglaciation sequence for the Windmill Islands was determined from the 14C age of raised marine shorelines, lakebottom sediments, and Adelie penguin remains found in abandoned rookeries. A north-south gradient in the elevation of the upper marine limit was observed, with the highest marine limit (31-32 m) observed on Browning Peninsula and Hull Island at the southern edge of the islands. Correspondingly, the southern islands were found to have been deglaciated by 8000 (corr.) yr B.P. while the northern islands were deglaciated by 5500 (corr.) yr B.P. Isostatic uplift rates were calculated as 0.5 to 0.6 m/100 yr, with an estimated total uplift of around 53 m which indicates late Pleistocene ice sheet thicknesses of 200 and 400 m over the islands and adjacent Petersen Bank, respectively. The margin of the Late Pleistocene grounded ice sheet extended an estimated 8-15 km offshore which coincides with the location of the 200 m isobath.

Implications of the Radiocarbon Timescale for Ice-Sheet Chronology and Sea-Level Change

A new extended radiocarbon calibration curve has allowed a reexamination of relative sea-level data based on pre-Holocene dates. At sites located far from any Late Pleistocene ice sheet, the effect of employing this new calibration curve is that the calibrated data (with ages up to 17,100 14C yr B.P.) now agree with the corresponding relative sea-level curve predicted by the ICE-3G deglaciation model. An important implication of this new calibration curve is that the last glacial maximum (ca. 18,000 14C yr B.P.) is inferred to have occurred 22,000-21,000 cal yr B.P. This allows for additional ice to be incorporated in a revised deglaciation model than suggested by ICE-3G. The predicted relative sealevel curves of this new model match the relative sea-level data as well as those of ICE-3G. Further, the total sea-level rise of 124 m at Barbados since the last glacial maximum predicted by this new model agrees with the estimated value of 121 ± 5 m obtained from the depths of drowned reef-crest corals.